The AT78C5001 is a 4-port serial ATA I host controller that provides a 64-bit PCI-X bus interface with an automatic DMA engine. The PCI-X to Serial ATA ADMA Host Bus Adapter is a single-chip solution for a PCI-X to serial ATA controller. It accepts host transaction requests through the PCI-X bus, processes them and transmits them to one of four serial ATA devices. The AT78C5001 supports serial ATA speeds of 1.5 Gbits/s of 8/10bit-encoded data that is equivalent to 150 Mbytes/s of raw data. The AT78C5001 derives its serial ATA clocks from an external source with a reference clock of 75 MHz. On the 64-bit PCI-X bus, when run at the maximum frequency of 133 MHz, it supports a maximum burst transfer rate of 1064 Mbytes/s. It embeds four ADMA process engines, two in each ATA channel. The ADMA mechanism drastically increases the performance of systems that use ATA devices. Its major benefit is CPU overhead reduction. The device ADMA engine offloa ds th e host pro ce ssor by au to ma ting the p rocess of sending comman d requests/retrieving responses for each of the requests and queued responses. The ADMA both reduces the host processor overhead and substantially increases the number of commands that can be loaded into the queue in the device.